The present invention is directed to a method for obtaining images by magnetic resonance imaging.
2. DESCRIPTION OF THE PRIOR ART
The following pulse sequence is described in the article entitled: "A New Steady-State Imaging Sequence for Simultaneous Acquisition of Two MR Images with Clearly Different Contrasts," Bruder et al., Magnetic Resonance in Medicine, Vol. 7, pages 35-42 (1988):
(a) In a time interval T.sub.R &lt;T.sub.2, RF pulses are generated in the z-direction with the simultaneous generation of a gradient G.sub.2. A magnetization condition which is known as SSFP (steady state free precession) thereby arises. PA1 (b) An inverted gradient pulse G.sub.z, is generated in the z-direction before and after each RF pulse. PA1 (c) A gradient G.sub.y in the y-direction and a gradient G.sub.x in the x-direction are generated before and after each RF pulse. PA1 (d) Two gradients in the x-direction are symmetrically activated between two RF pulses, with a signal being read out under each of the two gradients. PA1 (e) The above sequence (a)-(d) is repeated n times, with the time integral of the gradient G.sub.y being varied in PA1 (f) The signal which has been read out is sampled, and two images having different T.sub.2 contrast are reconstructed from the sampled measured values.
equidistant steps.
The above method combines a FISP sequence and a sequence which is mirror-symmetrical to the FISP sequence (referred to below as the PSIF sequence) into a singe pulse sequence, whereby two images having highly different T.sub.2 contrast are obtained.
PSIF sequences are especially useful for measuring T.sub.2 -weighted images. This is of particular significance for the display of CSF (cerebral spinal fluid) in the head and in the spinal column. CSF, however, exhibits a pulsating motion, so that pulsation artifacts are present in the image obtained using the PSIF sequence.